This research program is designed to examine the selective importance of allozymic variation in natural populations. This will be done by concurrent evaluation of patterning of variation in nature and the kinetic examination of alternative allozymes in the laboratory. It is anticipated that this combined approach will provide a firmer base in enzyme function for statements about the importance of selection than is usually possible when either approach is separately applied. While examination of particular enzymes cannot settle the general question of the importance of selection at the allozymic level, it can provide a much more complete picture for particular cases than ordinarily formed. And by accumulation of several integrated case studies we may expect to see some generality concerning the question emerge. I propose an examination of a one-locus, two-allele polymorphism for phosphoglucose isomerase in populations of the sea anemone Metridium senile. Patterns of variation will be examined along the New England coast by electrophoresis. Allozyme types will be purified by standard methods and evaluated kinetically for differences in behavior with pH, ionic strength, and temperature, any of which may be of selective importance in nature. Synergism between kinetics and field studies is anticipated, each aspect providing input to the other. I anticipate contributions to general knowledge concerning processes of adaptation and population genetics.